PLANTS I Green algae- Charophyceans (closest relatives to plants) Evidence supporting relationship Similar Characteristics • Protists (algae) are similar to plants by : multicellular, eukaryotic, photosynthetic autotrophs • Plants have : cellulose in their walls and so do green algae, dinoflagellates, and brown algae. And chloroplats with chlorophylls a and b 4 Key traints that land plants share only with charophyceans 1. Rose shaped complexes for cellulose synthesis - The cells of both l.plants and Charophyceans have rosette cellulose synthesizing complexes. These are rose shaped arrays of proteins in the plasma membrane that synthesize the cellulose of the cell walls. (noncharophycean algae have linear arrays) - Cell walls of plants and charophyceans have higher percentage of cellulose compared to others - Differences indicate that cellulose walls in plants and charophyceans evolved independently of those in other algae 2. -Peroxisomes of both land plants and charophyceans contain enzymes that minimize the loss of organic product 3. Structure of flagellated sperm (same between the two) 4. Formation of a phragmoplast (Same cell division) - The synthesis of new cross walls during cell division involves the formation of a phragmoplast Mickle Notes • Same pigments and chlorophyll's between the two • Food storage= Startch (also in green algae) • Green algae have the same number of cell divisions Adaptations Enabling the move to land • Green algae inhabit shallow waters • Natural Selection favors individual algae that can survive when not in water • In green algae, a layer of durable polymer called sporopollenin prevents exposed zygotes from drying out • Environmental changes- brighter sunlight, atmosphere had an abundance of CO2, soil was rich in nutrients, fewer herbivores and pathogens PLANTS I Traits of Plants • 5 key traits absent in green algae a. apical meristems b. Alternation of generations c. Walled spores produced in sporangia d. Multicellular gametangia e. Multicellular, dependent embryos A. Apical Meristems Roots and shoots can elongate, increasing exposure to environmental resources This growth in length is sustained throughout the plant’s life by the activity of : Apical meristems- localized regions of cell division at the tips of shoots and roots - Cells produced y apical meristems differentiate into various tissues, including a surface epidermis's that protects the body and several types of internal tissues. B. Alternation of Generations Life cycles of land plants alternate between 2 different multicellular bodies It does not occur in charophyceans. We can infer that it is a characteristic derived of land plants- it was not present in the ancestor common to land plants and charophyceans Alternation of generations is distinguished by the fact that there are both multicellular haploid and diploid stages in their life cycle The 2 multicellular forms that alternate in the cycles are: Gametophytes and Sporophyte generations: • Gametophyte cells are haploid, its named for its production by mitosis of haploid gametes (egg and sperm) that fuse together forming diploid zygotes ... Mitotic division of the zygote produces the multicellular: • Sporophyte, thus those cells are diploid. Meiosis in a mature sporophyte produces haploid spores- these cells can develop into a new organism without fusing with another cell • Gametes cannot develop directly into a multicellular organism, but are ment to fuse and form zygotes • When a spore undergoes mitosis, it makes a new multicellular gametophyte and so the cycle continues from there. C. Walled spores produced in the Sporangia Sporopollenin makes walls of plant spores very tough and resistant to harsh environments, this chemical adaptation makes it possible for spores to be dispersed through dry air without harm. A Sporophyte contains a sporangium, within that exist diploid cells called sporocytes (spore mother cells) undergo meiosis and generate those haploid spores PLANTS I Charophyceans also produce spores, but these algae lack multicellular sporangia and their flagellated, water dispersed spores lack sporopollenin D. Multicellular Gametangia Production of gametes within gametangia is another feature of land plants and not their algal ancestors. The female gametangia are called archegonia, each of which are a vase shaped organ that produces a single egg retained within the base of the organ. Male gametangia called antheridia produces and releases sperm into the environment. Each egg is fertilized within an archegonium where the zygote develops into an embryo, E. Multicellular, Dependent Embryos Embryos develop from zygotes, and are retained within tissues of the female parent. The parental tissues provide the embryo with nutrients, such as sugars and amino acids. The embryo has specialized placental transfer cells- sometimes present in the adjacent maternal tissue as well- which enhance the transfer of nutrients from parent to embryo though the elaborate ingrowths of the wall surface (plasma membrane and cell wall). This trait is so significant and derived from land plants that they are also known as embryophytes. • These traits were absent in the ancestor common to land plants and Green Algae • Set land plants apart from their closest algal relatives Other traits that relate to terrestrial plant life are: 1. Greater risks of desiccation (drying out)-- their surfaces have a cuticle, that consists of polymers called polyesters and waxes. Acts as waterproofing, and protects against microbial attack 2. Many land plants produce molecules called secondary compounds, Includes: alkaloids, terpenes, tannins and phenolics such as flavonoids. - various alkaloids, terpenes and tannins have a bitter taste, strong odor or toxic effect that help defend against herbivores and parasites - Flavonoids absorb harmful UV radiation and may act as signals in symbiotic relationships with beneficial soil microbes - Phenolics deter attack by pathogenic microbes - Humans also benefit from secondary compounds, (ex. alkaloids that can fight malaria) Origin and diversification of plants • Fossil spores dating up 475 mya • Some spores are different from typical land plants - spores of living plants dispersed as single grains, but fossil spores are fused together in groups of 2 or 4 - Raises the possibility that the fossil spores were not produced by plants, but by some extinct algal relative • The oldest known fragments of plant tissue are 50 million years younger than the puzzling spores PLANTS I Land Plants Grouping Based on the presence or absence of vascular tissue - cells joined into tubes that transport water and nutrients throughout the plant body. • Vascular plants - have a complex vascular tissue system. • Non vascular plants: plants that do not have an extensive transport system (ex. liverworts, hornworts, moss) ( some moss have simple vascular tissue) • Non-Vascular plants are often informally called bryophytes (meaning moss-plant in greek). Whether or not bryophytes are monophyletic, they share some derived traits with vascular plants such as: multicellular embryos, and apical meristems (but they lack true roots and leaves) • Vascular plants form a clade, and consist of about 93% of all plant species. They can be further characterized into 3 smaller clades. 2 of these clades are the • Lycophytes (club moss and their relatives) ..and.. • Pterophytes(ferns and their relatives). Each of these clades lack seeds, which is why collectively the two clades are often informally called seedless vascular plants. The third clade are seed plants, the vast majority of living plants species. A seed is an embryo packaged with a supply of nutrients inside its coat. Those seed plants can then be divded into 2 groups, Gymnosperms and angiosperms. Based on the absence or presence of enclosed chambers in which seeds mature. • Gymnosperms- are grouped together as “naked” seed plants. Their seeds are not enclosed in chambers. Of these surviving species include conifers, probably form a clade • Angiosperms- are a huge clade consisting of all flowering plants. Angiosperm seeds develop inside chambers called ovaries, which originate within flowers and mature into fruits. The life cycle of moss and other bryophytes are dominated by the gametophyte stage 3 small phyla of herbaceous (non-woody) plants that represent bryophytes are: a. Liverworts (phylum hepatophyta) b. Hornworts (phylum anthocerophyta) c. Moss (bryophyta) A and B are named after their shape, wort means herb. Mosses are our most familiar bryophyes, although some plants commonly called moss are not really moss at all. (this includes irish moss (a red type of sea weed), reindeer moss (a lichen) and club moss (seedless vascular plants) ..Don’t Confuse PLANTS I Bryophyta is the formal taxonomic name for the phylim, and only means mosses. Bryophyte is used informally to refer to all nonvascular plants (a,b and c) Note: it is not established if (a,b, and c form a clade) Living bryophytes reflect some traits of the earliest plants, and have many unique adaptations. The oldest known fossils of plant fragments as ex. have the same type of tissue as liverworts. Bryophyte Gametophytes • In bryophytes (all 3) have larger and longer living gametophytes than sporophytes. Sporophytes are present in only part of the cycle time. • If spores are dispersed in a favorable habitat, (moist soil or tree bark) they may germinate and grow into gametophytes. • In moss spores, they characteristically produce a mass of green, branched, one cell thick filaments known as protonema. A protonema has a large surface area that enhances absorption of water and minerals. - in favorable conditions, a protonema produces one or more “buds” each with an apical meristem that generates a gamete-producing structure known as a gametophore. Together, a protonema and gametophore make up the body of a moss gametophyte. Gametophytes have ground hugging few celled thick carpets, that can’t really support tall plants.Bryophytes also don’t have vascular tissue, which is required for long distance transport of water and nutrients, so it’s not that tall. Rhizoids anchor gametophytes, they are long, tubular single cells (in liverworts and hornworts) or filaments of cells (in moss). Unlike roots, rhizoids are not composed of tissuies, lack specialized conducing cells and do not play a primary role in water and mineral absorption. Mature gametophytes produce gametes in gametangia covered by protective tissue. A gametophyte may have multiple gametangia. Eggs are produced singly in archegonia, where antheridia makes sperm. Some bryophyte gametophytes are bisexual, but in moss the archegonia and antheridia are typically carried on separate F and M gametophytes. Flagellated sperm typically swim through a film of water towards eggs, entering the archegonia (attracted to chemicals). Eggs are not released but instead remain within the base of the archegonia. layers of placental transfer cells help transport nutrient's to the embryos as they develop into sporophytes. Bryophyte Sporophytes Sporophytes are usually green and photosynthetic when young and cannot live independently. They are attached to their parental gametophytes and absorb nutrients. (sugars, amino acids, minerals and water) Of all the plant groups, bryophytes have the smallest and simplest sporophytes (gives truth to the hypothesis more complex sporophytes evolved later in vascular plants). PLANTS I A sporophyte consists of a foot, seta, and a sporangium. Embedded in the archegonium, the foot absorbs the nutrients from the gametophyte. The seta, is the stalk, and conducts the materials to the sporangium, which is also called a capsule, and from there produces spores by meiosis. The seta is elongated in moss for better spore dispersal. An immature capsule has a protective cap of gametophyte tissue called a calyptra, which is shed when the capsule is mature. The upper part of the capsule sometimes contains a ring of toothlike structures known as the peristome. Its specialized for gradual spore discharge, using wind that can carry spores. Hornwort and moss sporophytes are larger and more complex than those of liverworts. Both Horn w. and moss have specialized pores called stomata, which are also found in all vascular plants. This suggests three possible hypothesis for their evolution. Liverworts (phylum hepatophyta) • liver-shaped gametophytes • described as “thalloid” because of the flattened shape of their gametophytes • Some are called “leafy” because their gametophytes have a stemlike structure with many leaflike appendages. • Found in tropical regions, they are much more common than thalloid species Hornworts-(phylum anthocerophyta) Shape refers to the sporophyte, which resembles a small grass blade The sporangium extends along its length and splits open to release mature spores, starting at the tip of the horn. Gametophytes grow horizontally and often have multiple sporophytes attached Moss (phylum bryophyta) • • • • • As opposed to the worts, moss grows vertically than horizontally gametophytes are the structures that primarily comprise a carpet of moss their “leaves” are usually only one cell thick, Moss sporophytes are typically elongated and visible to the naked eye though green and photosynthetic when young, they turn tan or brownish when ready to release spores Ecological and Economic Importance of Moss • Some moss can inhabit such extreme environmental conditions such as mountaintops, tundra and deserts • Many exist in very cold or dry habitats/c they can survive the loss of most of their body water, then rehydrate when moisture is available PLANTS I • Phenolic compounds in moss cell walls absorb levels of radiation present in deserts or at high altitudes and latitudes Peat moss, • or Sphagnum, is a wetland moss and produces partially decayed organic material known as peat • Because of the phenolic compounds embedded in its cell walls, sphagnum does not decay readily. It also secretes compounds that may reduce bacterial activity. • Low temp. and nutrient levels in peat bogs also inhibit decay. As a result, peat bogs can preserve mummified corpses for thousands of years In a larger scale... • 400 billion tons of organic carbon are stored in peat. These carbon reservoirs help stabilize global atmospheric CO2 concentrations • Peat is also a fuel source in europe and asia, it can also serve as soil conditioner and is used for packing plant roots during shipment